Cooling water restrictor

Can anyone offer some clarity on this please? I have searched the topic and came across this ref on here with the title Cooling/Heater Mod Fix from 11+ years ago.
Now, as far as I can understand it the PRT system has a 8mm diameter restrictor positioned in the 4-way "T" that connects to the steel water rail.
In the topic referred to above i.e.  MGF & MG TF Owners Forum - Cooling/ Heater Mod fix -
It suggests that the 2002/3 systems with the earlier thermostat position i.e. pre PRT would make use of the complex 4 way hose hose item shown in #128721 of that topic.
My understanding is that the transition piece in that complex hose (with the top hat reducer/connector in the top) simply provides a facility to fit the smaller hose and in doing so also restricts the flow to header tank.
But if converting to the PRT system that restriction in that position is not what is intended or needed. So whilst a hose kit (in silicone) might offer hoses to adopt either piping configuration the reducer at the steel pipe/water-rail is also essential simply because the guts have been taken out of the thermostat and the flow patterns have been adjusted to deliver better steady overall temperatures (or the heater only works at high rpm).
Can anyone offer a definitive conclusion on this please?
 

As I understand when the stat is removed after fitting the PRT conversion, so what others have done is to remove the centre of the normal removed stat then refit it to act as a reducer/restrictor. I would have done this had I decided to go the PRT route. Glyn.

Glyn, whilst the “hole” created in the thermostat by cutting the “gizzards” out of it is part of the solution it is only part of the equation controlling the flow via fluid balance.
But upstream of that on the by-pass circuit where the hose locates onto the steel coolant rail local to the “near side” end of the engine there should be another much smaller bore reducer.
The need for this as far as I can see is associated with different flow directions through the system and the need to push the water through the heater when it is called for.

if converting to Prt and retaining that complex moulded part I believe there is still a need for the additional restrictor, and if deploying a 4-way “T” I can’t explain why a jiggle valve is not included.
I’m really seeking clarity on all this.

Hi I don't think you will find one of those restrictors and as I said I would have gone ahead without it. This is one of the reasons I didn't because of the lack of parts for the conversion. G.

This aspect of the system wasn’t discussed when I changed to a PRT so just wapped it in as per David’s information. I’ve done a fair number of miles & until this cropped up , I would have remained ignorant. I’ll continue to bury my head in the sand, the view is better than you might think.
If you are desperate & have the dimensions, I can make you one.
M

Airportable that is a very generous offer. I believe I have some plastic rod that would do the job.
But I’ll see what I can do here at home first.

From Roger Parker’s book I know the bore (8mm). He says it is 17 mm long I think but what I do not know is which part is 17mm long nor what the OD is . I believe It has to rest against the end of the water rail (a diameter I don’t know yet until I start the job).
I guess it needs to be a push fit into the end of the water rail to keep it stable in operation.
In the images I have seen the thing enters the 4-way T but I can’t think that is correct otherwise the force of water pushing against it would tend to displace it - which is why I think it goes the other way.
So more research before committing to production.

Back to jiggle valves for a moment. I suspect that the hose configuration in the pre PRT set up made one essential as the hose was n shape to accommodate the configuration. The PRT arrangement with the 4-way T does not have that “n” raised feature avoiding the problem of bleeding air out of that high point. You can debate the need for one at the engine and opinions vary. My thoughts on that are that if it works it must be worth having. If it blocks that is different matter!